1. Field of the Invention
This invention relates to computer system architecture and, more particularly, to a system architecture for cache based systems to improve the floating point performance of such systems.
2. History of the Prior Art
Caches are used in computer systems to speed the overall operation of the system. The theory of a cache is that a system attains a higher speed by using a small portion of very fast random access memory (RAM) as a cache memory along with a larger amount of slower main memory RAM. If data and instructions are called from main memory and placed in cache memory as they are required by the program, and if the system looks first to the cache to see if the information required is available there, then the system will usually find the information desired in the cache and will, consequently, operate at a speed as though it were made of mostly high speed cache memory. This occurs because, statistically, information in any particular portion of a process which has just been used is more likely to be required immediately than is other information which has not been recently used.
This assumption has proven true, in general, so that in a well designed caching system the information desired is found in the cache over ninety percent of the time. On the other hand, the assumption is most accurate when describing the operation of a cache with the instructions of a particular process and is least accurate when applied to the retrieval of data, especially scientific data. This appears to be true because of the nature of the particular information sought. For example, in executing a process instructions are often repeated over and over again to carry out a single operation. Data, on the other hand, appears to be less likely to be selected in such a manner without change. Moreover, scientific data is often stored in the form of floating point information which requires for its storage substantially more actual storage space than do individual instructions. For example, a floating point number may require a double word space for storage in a typical computer system. Moreover, the tendency of scientific programmers is to arrange data in large arrays. Typically such arrays require so much memory storage space that the entire array cannot be placed in the typical cache memory space of a typical computer system. For the foregoing reasons, cache based systems have not proven as capable in speeding the operation of computer systems used in the processing of scientific information, especially processing involving large amounts of floating point numbers.